1. Field of the Invention
The present invention relates to a class of unsaturated polyester compositions termed hybrid resins. The term "hybrid" refers to the incorporation into a single new polymer the chemical groups and properties of two different polymer species.
2. Description of the Prior Art
Hydroxyl terminated unsaturated polyesters can be cured by reacting these resins with polyfunctional isocyanates and either concurrently or in a separate step, cross-linking the polyester via the unsaturated groups with a reactive ethylenically unsaturated monomer using a radical initiator. Hybrid resins of this type are described in the following papers:
(1) High Performance Urethane Modified Unsaturated Polyesters, H. R. Edwards, presented at the British Plastics Federation (1984);
(2) Hybrid Resins, undated publication of Amoco Chemical Corp.;
(3) The Use of Isophthalic Unsaturated Polyester Urethane Hybrids in Conventional Molding Techniques, H. R. Edwards, proceedings of the SPE 44th Annual Technical Conference and Exhibit, pages 1326-1330 (1986);
(4) Handling and Physical Properties of Hybrid Polyesters, H. R. Edwards, 39th Annual Conference, Reinforced Plastics Composite Institute, The Society of the Plastics Industry, Session 8-C, pages 1-8 (January 1984);
(5) Isocyanate Thickened Sheet Molding Compound, E. J. Thompson, L. M. Abevino and W. J. Fomissy, 37th Annual Conference, Reinforced Plastic Composite Institute, The Society of the Plastics Industry, Session 1-A, pages 1-6 (January 1982).
Of the above papers, paper number (1) relates to hybrid resins formed from various molar ratios of maleic acid to isophthalic acid in the unsaturated polyester. Paper number (2) describes the preparation of various hybrid resin molded compounds in which the polyester used has various ratios of polyol to acid. Paper number (3) discloses various hybrid molding compositions at different ratios of maleic acid to isophthalic acid in the polyester. Paper number (4) discloses the physical properties of various hybrid polyesters. Paper number (5) discusses the use of hybrid resins in various molding compositions using different fillers.
Compositions of the type described in the foregoing papers by Edwards when cured, tend to shrink unduly, which has limited their commercial application. For example, when attempts were made to use polyester isocyanate styrene compositions of the types described in the prior art to make a molded shell on a bowling ball, such attempts were unsuccessful. This was because the shell on the bowling ball cracked upon curing. The high degree of shrinkage of such previously described compositions upon curing also renders them unsuitable for many other applications as such shrinkage can cause reinforcing glass fibers to become visible at the surface and lead to a poor surface smoothness, or it can cause cracks to form in non-reinforced molded articles.
U.S. Pat. No. 4,595,725 to Hess et al discloses polyester resins formed from at least two glycols and at least one branching agent and a dicarboxylic acid residue containing fumaric acid residues.
U.S. Pat. No. 3,318,727 to Boenig et al discloses a polyester polyisocyanate composition for use as a bowling ball outside cover. The molar ratios of isophthalic acid and maleic acid shown in Boenig differ from those in the present invention.
U.S. Pat. No. 4,228,251 to Maekawa et al, discloses a resin composition containing polystyrene with unsaturated polyester resins to provide a stable complete one-pack type resin composition having low shrink properties.
U.S. Pat. No. 3,455,857 to Holzrichter, discloses vinyl modified alkyd or urethane resin compositions including a novel intermediate.
U.S. Pat. No. 3,806,490 to Kajiura et al, discloses a prepolymer polyester-polybutadiene composition used to produce shaped articles described as being free from cracks.
U.S. Pat. No. 4,242,415 to Feltzin et al, describes various amine terminated liquid polymers having an average of about 1.7 to 3 amine groups per molecule.
U.S. Pat. No. 4,287,116 to Burns, described the use of vinyl ester urethane resins for high impact strength applications such as automobile bumpers.
French Patent No. 1,477,822 to Reichhold-Beckacite, cited in Chemical Abstracts, Vol. 68: 3541S (1968), relates to various polyester resins which are modified by reaction with isocyanate.
British Patent No. 1,110,537 to Dayton Research, cited in Chem. Abs. 68:115428s (1968), discloses that unsaturated polyesters are treated before or during cross-linking with an amount of diisocyanate equivalent to the free hydroxyl groups in the polyester.
Japanese Patent No. 15316 (1966) to Toyo Rubber Industry Co., cited in Chem. Abs. 66:38420U (1967), discloses reacting unsaturated polyesters containing terminal hydroxyl groups with polyfunctional organic isocyanates and then reacting the products with vinyl monomers.
U.S. Pat. No. 4,584,363 to Goel et al, discloses thermoset resins made from polymerizing a mixture of a polyol from the reaction of an olefinically unsaturated polycarboxylic acid and bicyclic amide acetal with a polyisocyanate and a vinyl monomer.
Japanese Patent No. 86/19619 to Hitachi Chemical Co., cited in Chem. Abs. 105:61515e (1986), relates to resin compositions comprising unsaturated polyester resins and epoxy resins thickened with a polyfunctional isocyanate compound.